Why nanotubes become resistive at high fields: Measurements of electron-phonon coupling strengths

Abstract:Transport measurements in carbon nanotubes have shown ballistic transport even at room temperature over micrometer lengths at low electric fields. A sudden onset of phonon scattering at high electric field prevents reaching the desired high current densities without heating losses . We present the first measurements of the magnitude of the electron-phonon scattering matrix elements for different phonon modes in carbon nanotubes which confirm the role of optical phonons in the onset of reduced mean free path in transport measurements. Our results show that the G+ has a significantly stronger e-phonon coupling matrix element than the low energy radial breathing mode. Our measurements were performed on carbon nanotubes suspended across etched trenches in air. The laser energy was scanned through the nanotubes’ E22 resonance while recording the Raman intensity for the different Raman modes. These measurements were repeated for different carbon nanotubes of different diameter and chirality. The e-phonon coupling strength for individual carbon nanotubes compared to carbon nanotubes in contact with other nanotubes will also be discussed, with implications for transport capabilities.

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